title: Reference range of fetal nasal bone length between 18 and 24 weeks of pregnancy in an unselected Brazilian population: experience from a single service.
abstract: OBJECTIVE
  To determine reference range of fetal nasal bone length (NBL) during the second trimester of pregnancy in a Brazilian population.
  
  
  METHODS
  This was a retrospective cross-sectional study with 2681 normal singleton pregnancies between 18 and 24 weeks of gestation. The NBL was obtained in the mid-sagittal plane of the fetal face profile using the following landmarks: nasal bone, overlying skin and the tip of the nose. The NBL was measured by placing the calipers in the out-to-out position. To assess the correlation between NBL and gestational age (GA), polynomial equations were calculated, with adjustments by coefficient of determination (R(2)).
  
  
  RESULTS
  The mean of NBL ranged from 5.72 ± 0.87 mm at 18-18 + 6 weeks to 7.45 ± 1.23 mm at 24-24+6 weeks of pregnancy. We observed a good correlation between NBL and GA, best represented by a linear equation: NBL = 0.080+0.276*GA (R(2 )= 0.16).
  
  
  CONCLUSIONS
  We established a reference range of fetal NBL in the second trimester of pregnancy in a Brazilian population.
authors.affiliation: Referral Center for Teaching of Diagnostic Imaging (CETRUS) , São Paulo-SP , Brazil .
authors.forename: Edward
authors.initials: E
authors.lastname: Araujo Júnior
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
authors.forename: Claudio Rodrigues
authors.initials: CR
authors.lastname: Pires
authors.forename: Antonio Fernandes
authors.initials: AF
authors.lastname: Moron
authors.forename: Sebastião Marques
authors.initials: SM
authors.lastname: Zanforlin Filho
mesh_terms: D000293:Adolescent; D000328:Adult; D001938:Brazil; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D009295:Nasal Bone / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D012016:Reference Values; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000592:standards*; D055815:Young Adult
keywords: Brazilian population; fetus; nasal bone length; reference range